The goal of this research is to use a well-characterized set of polymorphic genetic markers (allozymes) in midwestern populations of Ascaris suum (Nematoda) as a benchmark for developing and characterizing the utility of a new methodology (RAPDs or Random Amplified Polymorphic DNA) that uses short (10-mer) primers and PCR to detect genetic polymorphisms among individuals. In addition, other selected helminth species will be used in pilot studies to test if protocols optimized for A. suum are applicable to other taxa. RAPD technology holds tremendous promise for the study of intraspecific variation among helminths and other medically important parasites. Because PCR is used to amplify targets from nanogram quantities of DNA, the RAPD technique has the potential to yield many more genetic markers than can be obtained by standard techniques such as allozyme electrophoresis. In addition, because DNA templates can be obtained from very small individuals, the RAPD technique may be applied to small helminths and other parasites when allozyme electrophoresis is not technically feasible. Potential applications of RAPD genetic markers to studies of parasites include: characterization and identification of strains; genome mapping; identification of conspecific life cycle stages; assessing levels of gene flow/genetic differentiation among populations; and identification of cryptic species. However, it is critical that well-researched methods are developed for applying the RAPD technique to helminths in order to establish criteria for scoring markers and analyzing the data. Such control experiments, optimized protocols, and general guidelines are best established before poorly designed and executed studies are published by reason of technique rather than scientific merit. The major advantage of using midwestern A. suum (pig ascaris) populations as a model fro obtaining RAPD data is that individual nematodes are both readily available and large enough so that polymorphic allozyme markers can be used to characterize independently the genetics of geographic variation in these populations. The apriori expectation is that these allozyme and RAPD markers should reveal the same general patterns of genetic variation over geographic space (although potentially on different scales); unpublished results show that ample genetic polymorphism is available for study by both RAPD and allozyme methods. Thus, midwestern A. suum populations can serve as an excellent model system for developing methods for the applications of RAPD technology to studies of helminth systematics.